Good question, for now, the false positive is not handled.
One solution is to keep a false positive whitelist (also a bloom filter) in server side, only when the first user reports the false positive url, the link will be joint into the whitelist, then timely distribute to client.

This is cool. I like that websites I visit won't get recorded by someone else however this needs to be open source. I no longer install Chrome plugins that are not open source or coming from very well known public companies.